This has happened to me a few times now.
I also lose the ability to toggle "Quick Selection" on/off with the space bar.
Restarting my Mac seems to solve the problem... till the next time.
Not a very complex project, but I only have 8 GB of Ram,.... so maybe?
Marc Corney, Architect
Red Canoe Architecture, P. A.
Mac OS 10.15.7 (Catalina)
Processor: 3.6 GHz 8-Core Intel Core i9
Memory: 48 GB 2667 MHz DDR4
Graphics: Radeon Pro 580X 8GB
ArchiCAD 25 (5010 USA Full)